This invention relates to gate valve construction and more particularly to the effectiveness and redundancy of sealing between the gate and seat members of the gate valve.
Prior art gate valves involve typically two seats separated by a gate in which the downstream seat is considered to be the reliable seal, and an unpredictable sealing characteristic is associated with the upstream seat. When upstream pressure in increased on these valves, a portion of fluid must pass across critical gate-to-seat or seat-to-body seal surfaces to pressurize the valve body cavity or chamber.
On valves with a rising stem, this fluid must be expelled across these same surfaces when opening the valve or high pressure is built up in the body cavity. This high body pressure is not only potentially damaging to the valve itself, but also makes the valve more difficult to operate.
Additionally, although there are two seats contacts the gate, there is little or no recourse to save the valve if either seat starts to leak.
Typical prior art patents of which illustrate the problem are shown in U.S. Pat. No. 3,768,774, U.S. Pat. No. 4,201,238, U.S. Pat. No. 3,026,084, U.S. Pat. No. 3,006,559, U.S. Pat. No., 3,696,831, and U.S. Pat. No. 4,281,819.